The multimedia broadcast multicast service (MBMS) is used for providing multimedia broadcast and multicast services for users in wireless cells. In a long term evolution (LTE) system, the MBMS can be provided in a frequency layer dedicated for the MBMS and a frequency layer shared with a non-MBMS. An LTE cell for supporting the MBMS can be either a dedicated MBMS cell or an MBMS/unicast mixed cell. Both single-cell transmission and multi-cell transmission can be used for the MBMS, but the multi-cell transmission of the MBMS is required to support a multicast broadcast single frequency network (MBSFN) transmission mode.
The MBSFN refers to the synchronization transmission in a plurality of cells with the same frequency at the same time. The MBSFN is adopted so as to save frequency resources and improve utilization rate of frequency spectrum. The plurality of cells are required to send the identical contents simultaneously so that the plurality of MBSFN cells can be regarded as one big cell by a user equipment (UE) receiver. Hence, Rather than being influenced by inter-cell interference from adjacent cell transmission, the UE is beneficial from superposition of signals from the plurality of MBSFN cells. The MBSFN transmission mode can be adopted by both the dedicated MBMS cell and the MBMS/unicast mixed cell. In addition, the time difference of multipath transmission can be solved by using an advanced UE receiver technology, thus eliminating inter-cell interference. A diversity effect caused by the same frequency transmission can be used to solve coverage problem and other problems so as to strengthen the receiving reliability and improve the coverage rate.
The technical characteristics of the multi-cell transmission of the MBMS are as follows: (1) the synchronous transmission of the MBMS in an MBSFN area, (2) supporting for combining multi-cell MBMS transmission, (3) mapping of a multicast traffic channel (MTCH) and a multicast control channel (MCCH) on MCH physical channels for point-to-multipoint (PTM) transmission, and (4) available semi-static configuration in an MBSFN synchronization area by, e.g., operation & maintenance (O&M).
Logical channels related to the MBMS transmission mainly include broadcast control channels (BCCHs), MCCHs and MTCHs. The main functions of the logical channels lie in as follows.
The BCCHs are used for broadcasting system information to the UE by network. In regard to the MBMS, configuration information (i.e. MCCH repeating period, offset of a start sub-frame, amount of occupied sub-frames, and PLC UM mode configuration, etc.) of the MCCHs is carried by the BCCHs so that the UE can find out the position of MCCH resource. While specific MBMS information is not carried in the BCCHs.
The MCCHs are downlink PTM channels and used for transmitting control information related to the MBMS in an MBSFN area to the UE by the network. One MCCH may correspond to one or more MTCHs (that is, the control information of the multiple MTCHs may be carried). The MCCHs may include configuration information (e.g. MSAP and period of MSAP occasion) of physical multicast channels (PMCH or MCH), MBMS radio bearer (RB) information (e.g. RBs provided in the update cycle of one MCCH), MBMS session Start, and MBMS Session Stop, etc.
The MTCHs are downlink PTM channels and used for sending specific MBMS data to the UE by the network.
The network uses the BCCHs to indicate the MCCH configuration information to the UE and then uses the MCCHs to provide MTCH information for bearing specific services for the UE. Thus, the UE can receive the MBMS on the MTCHs.
The relation between an MBMS area and the MBSFN synchronization area is shown that the MBMS area is composed of one or more service identifier, each of which is mapped into one or more cells. And the MBMS area is taken to an eNB by a broadcast-multicast service center (BM-SC) in a session message. The MBSFN area comprises one group of cells which carry out synchronous transmission of the MBSFN in the synchronization area. And the MBSFN area is planned by a multicast coordination entity (MCE) in accordance with strategies of operators and is notified to the eNB in an M2 interface message. The reserved cells of the MBSFN area belong to the synchronization area and do not carry out transmission of the MBSFN.
In the prior art, the eNB configures MBMS areas belonging to the cells by O&M and then notifies the MCE by an M2 setup request message, and the MCE allocates MBSFN area identities in accordance with the strategies and returns to the eNB. However, the MBSFN area may be different from a service area, so the corresponding relation between the MBMS control information and service information should be clarified when those two are transmitted, otherwise, different understandings on different eNBs in the MBSFN area will result in the failure of synchronization of control information related to the MCCHs.